Based on the previously discussed differences, I am going to develop a custom workflow to implement this requirement. The following screenshot shows the workflow process diagram that we need to implement:

When a QA associate creates an issue record, he will add basic information related to the issue. He will also select the project team in the project team member lookup. Once he saves the issue record, we will start the issue assignment workflow. The issue assignment process will find out the team member who has the least issues assigned and assign the issue to that member. Once the issue is assigned, our workflow will send a notification to the concerned team member about the issue assignment.